Here's a screenshot of how the menu looks for me on macOS 10.15.4 and Textastic 4.0.3.

Cmd-V is definitely there, I use it all the time. Have a look at the menu Edit -> Paste.

Interesting, I haven't seen this article before. By the way: it is possible to copy the selected files to another folder, not just moving them. "Copy To..." is an option in the menu that comes up when you tap the three dots button ("...") after selecting files. 

As a workaround, after tapping the Edit button, you can drag one finger over the checkmark circles on the left of each file. Don't lift your finger but swipe right down to the end of the list over the toolbar and it will automatically scroll down and select all files. 

It should be fixed in Textastic 9.2.

Thank you, I could reproduce the problem. It will be fixed in the next update.

I'm glad to hear that it works now. 

I'm aware of a crash when you have a beta version of iOS 13.4 installed. Installing the release version fixes the problem.

Which iPadOS version is installed?